The present invention relates to a valve having a valve body and a gate element wherein the gate element is movable to interrupt a flow passage passing through the body.
Typically in a valve of this general type, the gate element comprises a flat plate having a flow aperture therethrough. The plate is movable perpendicular to the flow passage between a first position where the flow aperture is in register with the flow passage, and a second position where the flow passage is out of register with the flow passage. This type of valve requires a cavity within the valve body to allow sufficient movement of the plate relative to the flow passage. It is possible that material can become lodged in the cavity and this can affect the performance of the valve. In extreme circumstances the build up of unwanted material can lead to the gate element becoming jammed thus rendering the valve inoperative. For example, in valves used in the oil industry waxy deposits and/or hydrate deposits can impede valve performance.
An alternative type of gate valve utilizes a gate element which is rotatable within the valve body about an axis parallel to the flow passage. By making the gate element circular and providing it in a correspondingly shaped circular cavity within the valve body, the free space in which material can accumulate is greatly reduced. Typically however, the gate element is required to be carried on a rotatable axle which is supported by, and projects into or through, the valve body. Examples of such valves can be seen in U.S. Pat. No. 917,970, U.S. Pat. No. 3,590,872, GB 2277573 and GB 2300896. This arrangement typically requires sealing means about the point through which the axle projects. Drive means are often coupled to the axle are also required to enable rotation of the gate member. The sealing and drive means increase the size, complexity and cost of the valve.
U.S. Pat. No. 5,284,320 describes a gate valve having a rotatable gate element. Rotation of the gate element is effected by an eccentrically rotatable pinion gear and an actuation gear surface provided in a cavity of the gate element. The gear surface has a cam shaped pitch line which co-operates with the eccentric movement of the pinion gear to rotate the gate element. This configuration requires the gate element to be constructed in two pieces comprising a first semicircular piece having a flow aperture therein, and a second semicircular piece having the actuation gear surface. Accurate machining is required to ensure an adequate fit between the pieces, and any imperfections in between the pieces can increase the friction between the gate element and the valve body. Furthermore, this type of valve requires a bush surrounding the gate element pieces to retain them in association with one another.
According to a first aspect of the present invention there is provided a valve comprising a valve body having a flow passage therethrough, a gate element having an orifice, and drive means to move the gate, wherein the gate is rotatably supported by a recess within the body and the valve body defines a pressure containing housing around the gate element.
By rotatably supporting the gate in the recess, the need for a shaft to carry the gate is eliminated. Accordingly the complexity of the valve is reduced. The overall size of the valve is also reduced making it suitable for applications where component size is an issue. An example of such an application is in the offshore oil industry where available space on oil platforms is limited. It is envisaged that a plurality of valves according to the present invention could be arranged together to provide, for example, a wellhead Christmas tree.
Preferably the gate element is disc shaped, and the recess is correspondingly shaped. In such an embodiment the free space between the gate element and the valve body is minimized and thus the possibility of material or debris lodging in the free space and consequently affecting the operation of the valve is reduced. The present invention also provides a gate element which rotates within a space substantially equal to its volume. In a conventional gate valve the gate element moves linearly within a cavity within the valve body, with the volume of the cavity being greater than that of the gate element. Debris can accumulate within the cavity when the gate element is in one position and can subsequently impede the gate element as it is moved to another position. The present invention seeks to eliminate the inherent disadvantages of having a cavity with a volume substantially greater than that of the gate element.
The drive means may be recessed in the valve body and or the gate element. In a preferred embodiment the drive means comprise a first member mounted for rotation in the valve body, and a second member mounted for rotation in the gate element, wherein the first and second members are linked such that rotational movement of the first member is transferred into rotational movement of the gate element by the second member.
In a preferred embodiment the first and second members are circular, and are mounted for rotation in correspondingly shaped recesses in the valve body and gate. In one embodiment the first member is provided with an eccentric pin and the second member is provided with an eccentric hole. Alternatively the first member may be provided with an eccentric hole and the second member with an eccentric pin.
In an alternative embodiment the drive means may comprise a rotatable member having an eccentric portion which is engageable in a slot provided in the gate element. The rotatable member may take the form of a disc having a pin extending from a face thereof. In an alternative embodiment the rotatable member may take the form of a cranked rod. In both cases, rotation of the rotatable member causes the eccentric portion thereof to bear against a wall of the slot and hence apply a drive force to the gate element. A sliding block or bush may be provided between the eccentric portion and the slot. The slot may be linear or curved.
In a further alternative embodiment the drive means may comprise a link member pivotally connected between the gate element and a rotatable member. In use, rotation of the rotatable member is translated into rotational movement of the gate element by the link member. In one embodiment, the rotatable member is in the form of a disc and the link member is pivotally connected eccentrically with respect to the disc.
In yet further embodiments the drive means may comprise a worm gear engageable with the gate element, or a toothed rack engageable with the gate element.
According to a second aspect of the present invention there is provided a drive mechanism for the rotatable gate of a valve, the drive mechanism comprising a first member mountable for rotation in a body of the valve, and a second member mountable for rotation in the gate, the first and second members being linkable such that rotational movement of the first member is transferred into rotational movement of the gate element by the second member.
Preferably the first and second members are circular, and are mounted for rotation in correspondingly shaped recesses in the valve body and gate. In one embodiment the first member is provided with an eccentric pin and the second member is provided with an eccentric hole. Alternatively the first member may be provided with an eccentric hole and the second member with an eccentric pin.
Preferably a drive shaft is provided to enable the first member to be rotated. Preferably the first member, the second member, and the gate are rotatable about axes which are mutually parallel.
According to a third aspect of the present invention there is provided a rotatable gate element for a valve, the gate element having an orifice and comprising a carrier member and two wedge members, the wedge members being carried by the carrier member, and each wedge member having opposing inclined wedge faces, wherein one of the wedge members is provided with a cam surface which, in use, is acted upon so as to move the wedge faces of the wedge members into contact with one another and hence move the wedge members relative to one another and outwardly with respect to the carrier member.
In a preferred embodiment the cam surface of the wedge member is acted upon by a corresponding cam surface provided on the body of the valve. Preferably the cam surfaces are caused to act upon one another by rotation of the gate element relative to the valve body. Preferably the outward movement of the wedge members urges the wedge members into contact with seats of the valve so as to ensure a leak tight seal between the seats and the gate element. The gate element is preferably disc shaped with the carrier member and wedge members being substantially semicircular.
The wedge members may be retained in association with the carrier member by means of pins or the like attached to each wedge member which pass through lugs of the carrier member.